The present invention relates to a wideband communication system for television signals which provides simultaneous two-way digital data communication between a central unit or distribution location and the various remote locations or subscriber units. The invention is particularly applicable to closed circuit and community or apartment antenna television systems, especially where automatic control and processing of for example, subscriber accounts and billing, subscriber requests and system monitoring or "polling" is desired. It is equally suitable for television antenna systems in, for example, hotels or hospitals where in addition to the distribution of television signals there is a requirement for automatic processing and accounting of patron service requests, room or patron status conditions and the like.
The first community antenna television systems were used in geographic areas where satisfactory television reception was not possible without the use of highly elevated or advantageously located directional and high gain antennas. The poor signal reception in these areas was usually due to adverse surrounding terrain resulting in signal shadow zones and/or excessive distance to the nearest television broadcast station. Because it was economically impractical for each television set owner in these fringe areas to install and maintain a suitable antenna system, a single advantageously located antenna array feeding a cable network for supplying each individual subscriber with a usable television signal came into use. In these early systems, the subscribers were usually limited in number as was the number of different television signals available for distribution; and as a result, the systems were simple in nature and the initial and recurring costs were minimal and subscriber fees and billing, if any, did not create problems.
With the increase in the number of television broadcasters and the greater increase in the number of television owners, distribution systems have become much more complex and costly. Illustrative of the present state of the art in these complex distribution systems are the patents to Face et. at. U.S. Pat. No. 3,668,307 and Moses U.S. Pat. No. 3,647,976. In addition, the realization that such systems have advantages in highly populated areas even where a substantial number of free television broadcast stations already exist results in systems which must serve many thousands of subscribers and distribute a considerable amount of program including special material requiring additional subscriber fees for its use or viewing. Such complex distribution systems require considerable supervision and control preferably as foolproof and automatic as possible and with a maximum of independence upon necessary subscriber actions.
It is therefore an object of the present invention to provide a cable television system which distributes either or both of commercial broadcast or "free" program material and "special pay" or "premium" program material.
It is another object of the present invention to provide for two way digital communication between subscribers and the network central unit simultaneous with the distribution of program material.
It is still another object of the present invention to provide a cable television signal distribution system which operation and functions are computer controlled and supervised.
It is a further object of the invention to provide a cable television distribution system which allows the subscriber to select at his discretion any of the several services provided by the system.
It is another object of the invention to provide a distribution system which performs accounting and billing functions for the type and amount of services utilized by each individual subscriber.
It is an object of the present invention to provide a cable distribution system which identifies subscribers in the system and accepts and facilitates commands or program requests from such subscribers.
Another object of the present invention is to provide each subscriber in the system with a specific time slot or group of time slots from which subscriber identification and message communication is possible without the need for special address communications.
An additional object of the present invention is to provide a subscriber control unit which recognizes its particular time slot by the counting of time slots.
Still another object of the present invention is the utilization of a time format which is digitally clocked and referenced to the commercial television scanning frequencies.
A further object of the present invention is to provide a television system, the "pay" or "premium" program material of which is scrambled or encoded to prevent unauthorized subscribers from benefiting therefrom and to periodically rearrange the coding sequence to further guard against unauthorized use.
The complexity of a television distribution system depends to a great extent on the amount of automation and control desired. In small systems with a limited number of remote locations and a limited amount of program material, it would not be economically feasible to install a highly automated and complex system such as those of the aforementioned patents when such a complex system is not required initially even though the more sophisticated system might be advantageous at a later date because of the increase in the number of subscribers and/or available program material and services.
Therefore it is another object of the present invention to provide a cable television system, the configuration of which is readily adaptable to expansion of control and function as the need arises.
Yet another object of the present invention is to provide an initially small scale economical installation having two way communication capabilities and premium program encoding which may later by expanded to meet growing subscriber needs without obsoleting the initial installation.